The present invention relates generally to the field of humidity probes, and more particularly to relative humidity probes for concrete.
Concrete is a common substrate for many commercial, industrial, and residential floors. Many types of floor coverings including wood, carpet, vinyl tile, sheet vinyl, and linoleum are commonly placed on concrete floors. Coatings such as epoxies, polyurethanes, and polymer-terrazzo, are widely used in commercial, governmental, educational, manufacturing, and health care facilities. These types of floor coverings are sensitive to moisture and prone to failure when excessive moisture is present. In addition to the floor covering materials, many modern water-based adhesives are prone to failure when excessive moisture and high pH are present. Furthermore, moisture also promotes fungal growths that can create significant odor and health problems. Typical moisture-related failures of floor coverings are curling, cupping, doming, shrinkage, blistering, and adhesion loss, all potentially leading to trip-and-fall hazards. In retail establishments, adhesive oozing at tile seams is unsightly and attracts dirt, leading to cleaning problems. In previous decades, the most commonly used asphaltic cut-back adhesives for vinyl tile were relatively insensitive to moisture. Polymer coatings and polymer terrazzo fail via osmotic blistering. Excessive moisture in concrete floors often delays construction, the installation of finish flooring and furniture, and ultimately occupancy, creating major problems for the floor covering and coatings industries.
To avoid moisture problems, floor covering and coating manufacturers specify a maximum moisture vapor emission rate (MVER) for concrete floors on which their products will be installed. The industry standard MVER specification is 3 to 5 lb./1,000 sq. ft./24 hrs. when measured by ASTM F1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride. This test is widely used: manufacturers of test kits have indicated that more than 300,000 test kits are sold annually in the United States. However, this test method has many interferences and shortcomings. Recognizing these problems, ASTM Committee F-6 on Resilient Floor Coverings adopted ASTM F2170-02, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes. This test method employs an electronic humidity sensor placed into a drilled hole in concrete, connected by a cable to a hand-held meter. This method was drawn from recent experience in Scandinavia and England, where relative humidity measurements in floors have been used for two decades. Building codes and Codes of Practice for installation of flooring in Europe have standards based on relative humidity. Flooring manufacturers in the United States are aware of this test method and are beginning to publish requirements for moisture as measured by relative humidity probes.
Commercially available relative humidity probes suffer from several drawbacks. First, they require time to equilibrate with the surrounding concrete. ASTM F2170 currently requires that drilled holes sit undisturbed for 72 hours before measurement, based on work at the Swedish Center for Building Research (Molina, 1990) and Lund University (Hedenblad, 1997). The larger the diameter of hole drilled, the longer the time necessary for the hole to equilibrate. Currently available probes require this long waiting period because the probes are of relatively large diameter: when a 16 millimeter diameter hole is drilled approximately 50 millimeters into concrete to accommodate the probe, the heat generated by drilling disturbs the moisture equilibrium in the region of the drilled hole. Time is required for the hole to re-equilibrate at service temperature and for moisture to equilibrate by diffusion within the region of the hole. Second, the “dead volume” within these probes, due to their size, requires time for moisture to diffuse and equilibrate within the probes. Third, temperature differences between the probe and the concrete require time for equilibration due to the heat capacity of the probes. All of these factors require the testing agency to wait several days to obtain test results, often when construction schedules are tight. Many of these problems stem from the relatively large size of current probes being used.
A second problem is that the current generation of instruments meeting ASTM F2170 have RH probes that are placed in concrete and separate hand held meters to which they are connected to obtain results. The meters are bulky, expensive, and can only be used with one RH probe at a time. One brand of meter requires that calibration factors for each probe be manually entered into the hand held meter one-at-a-time before use, and only up to ten such factors can be accommodated in the meter. A user must be familiar with the handheld meter to be able to determine the relative humidity.
A third problem is that the current generation of probes all protrude from the drilled holes in the concrete, making them susceptible to damage from construction traffic or building usage, or even present safety dangers to construction workers or other passersby. Probes often are broken or damaged beyond repair due to this problem. In addition, this protrusion makes current probes unsuitable for long term use or for intermittent use throughout the life of a building.
A fourth problem is that the probes require cylindrical sleeves be inserted into the holes to shield the probes from concrete except at the bottom of the hole where it is desired to make the RH measurement. Sleeves must be purchased separately and carried to the jobsite for installation. Sleeves wear out after several uses and must be replaced.
Thus, there is a need for a probe able to make accurate relative humidity measurements following the procedures outlined in ASTM F2170, but make them much more rapidly and conveniently, with less likelihood of damage to the RH measuring devices.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.